• 한국공작기계학회논문집
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• 제15권2호
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• pp.51-58
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research works is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stain-stress behavior and the hardness of the welded part are investigated. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding qualify is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• 한국소음진동공학회논문집
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• 제25권7호
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• pp.510-517
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• 2015

The free vibration and stability analysis of a spinning composite shaft modelled as a thin-walled closed beam is performed for several design parameters, such as ply angle, aspect ratio, and spin speed. The governing equations of spinning shafts based on the Timoshenko beam theory are derived via Hamilton's variational principle. Coriolis acceleration and anisotropy of constituent materials are incorporated in the derivation. The equations of motion are then transformed to the standard form of an eigenvalue problem for free vibration and stability analysis. Analytical results both for uniform circular cylindrical shaft and rectangular cross-section shaft are obtained by using extended Galerkin method, and the results are compared with those from FEM ANSYS analysis for a verification.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.17-18
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• 2006

Laser welding of metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research works is to investigate the influence of the process parameters, such as the welding for metals with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the butt welding, the welding quality of the cut section, stain-stress behavior and the hardness of the welded part are investigated. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding quality is 1400W of the laser power, 0.8m/min, 0.9m/min of welding speed and $4{\ell}$ in of pressure for shielding gas.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.93-96
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• 2008

이 논문은 근단층지반운동(NFGM)하에서 내진성능을 평가하기 위한 RC교각의 진동대, 준정적, 유사동적 실험을 다룬다. 5개의 실험체가 수행되었다. 축소 모형을 제작하고 상부구조물의 중량 에 의한 축력의 효과는 프리스트레스에 의해 구현하였다. 지진이 발생할 때 상부 구조물의 횡방향 관성력은 진동대의 제한된 용량 때문에 교각 실험체에 연결한 질량 프레임으로 모사하였다. 특히, 진동대 실험에서 질량 모사 프레임이 교각 모델과 같은 변위로 움직이면서 마찰 효과를 최소화할 수 있도록 고려하였고 이에 대한 검증을 실시하였다. RC교각의 축소 계수를 4.25로 설정 하였다.

• 한국주조공학회지
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• 제19권5호
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• pp.427-432
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• 1999

Most investment castings contain some porosities and microcavities. In this study, we investigated the elimination trends of various internal defects in IN738LC investment castings for industrial gas turbine blade by hot isostatic pressing. The results showed that cylindrical defects which are under $0.6mm{\Phi}{\times}7mm$ size are mostly eliminated and aspect ratio of defects is more sensitive factor than their cross section shape in removing these defects. Increasing hot isostatic pressure and holding time doesn't affect the elimination trend of cylindrical defects over $0.6mm{\Phi}{\times}7mm$ size because first step(plastic deformation) of HIP densification doesn't occur under these HIPping conditions.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.997-1003
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• 2005

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research works is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding qualify of the cut section, stain-stress behavior and the hardness of the welded part are investigated. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding quality is 1600W of the laser power, 0.85m/min of welding speed and 4m/min of pressure for shielding gas.

• Structural Engineering and Mechanics
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• 제34권2호
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• pp.175-188
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• 2010

This paper deals with the buckling and postbuckling responses, and the progressive failure of square laminates of symmetric lay-up with a central rectangular cutout under in-plane shear load. A detailed investigation is made to show the effects of cutout size and cutout aspect ratio on the buckling and postbuckling responses, failure loads and failure characteristics of $(+45/-45/0/90)_{2s}$, $(+45/-45)_{4s}$ and $(0/90)_{4s}$ laminates. The 3-D Tsai-Hill criterion is used to predict the failure of a lamina while the onset of delamination is predicted by the interlaminar failure criterion. In addition, the effects of boundary conditions on buckling loads, failure loads, failure modes, and maximum transverse deflection for a $(+45/-45/0/90)_{2s}$ laminate with and without a square cutout have been presented. It is concluded that because of early onset of delamination at the net section of cutouts before first-ply failure, total strength of the laminate with very small cutouts can not be utilized.

• 콘크리트학회논문집
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• 제25권6호
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• pp.601-612
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• 2013

거대한 벽체를 사용하는 원전구조물의 건설에서, 시공성과 경제성향상을 위해 벽체의 전단철근으로 사용되는 고강도 철근의 사용이 필요하다. 이 연구에서는, 550 MPa 급 철근을 사용한 낮은 벽체(형상비 1.0)의 전단내력과 변형능력을 검증하기 위해 벽체의 반복하중재하 실험이 수행되었다. 실험 변수는 수평철근의 항복강도(550 MPa 급, 420 MPa 급), 콘크리트 압축강도(46 MPa, 70 MPa), 수평/수직전단철근비, 횡구속후프의 여부, 벽체의 단면형상, 파괴모드(휨항복 전 또는 후 전단파괴)였다. 실험결과를 420 MPa 급 철근을 사용한 벽체, 그리고 현행설계기준에 의한 예측강도와 비교하였다. 실험 결과로부터 550 MPa 급 철근을 사용한 벽체의 전단강도가 420 MPa 급 철근을 사용한 벽체의 전단강도에 비해 안전여유가 조금 감소하였으나 비슷함을 보였다. ACI 349 전단강도식은 550 MPa 급 철근을 사용한 벽체를 과소평가하였으며, 휨 항복의 실험체의 경우 큰 변형능력을 보였다. 이 결과는 ACI 349 규정이 550 MPa 급 철근을 사용한 낮은 벽체(형상비 1.0)의 내진설계에 안전하게 적용될 수 있음을 가리킨다.

• Wind and Structures
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• 제30권5호
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• pp.525-532
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• 2020

This work numerically investigates the effects of Reynolds number Re_D (= 100 - 150), cross-sectional aspect ratio AR = ( 0.25 -1.0), and attack angle α (= 0° - 90°) on the forces, Strouhal number, and wake of an elliptical cylinder, where Re_D is based on the freestream velocity and cylinder cross-section height normal to the freestream flow, AR is the ratio of the minor axis to the major axis of the elliptical cylinder, and α is the angle between the cylinder major axis and the incoming flow. At Re_D = 100, two distinct wake structures are identified, namely 'Steady wake' (pattern I) and 'Karman wake followed by a steady wake (pattern II)' when AR and α are varied in the ranges specified. When Re_D is increased to 150, an additional wake pattern, 'Karman wake followed by secondary wake (pattern III)' materializes. Pattern I is characterized by two steady bubbles forming behind the cylinder. Pattern II features Karman vortex street immediately behind the cylinder, with the vortex street transmuting to two steady shear layers downstream. Inflection angle α_i = 32°, 37.5° and 45° are identified for AR = 0.25, 0.5 and 0.75, respectively, where the wake asymmetry is the greatest. The α_i effectively distinguishes the dependence on α and AR of force and vortex shedding frequency at either Re_D. In Pattern III, the Karman street forming behind the cylinder is modified to a secondary vortex street. At a given AR and α, Re_D = 150 renders higher fluctuating lift and Strouhal number than Re_D = 100.

• 한국터널지하공간학회 논문집
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• 제16권3호
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• pp.287-298
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• 2014

본 연구에서는 TBM 터널 SFRC 세그먼트 개발을 위하여 이형철근이 보강되지 않은 SFRC 보의 휨파괴 실험을 통하여 SFRC 배합의 평가를 수행하였다. 압축강도, 강섬유의 형상비와 강섬유 혼입률을 변수로 하여 총 16개의 SFRC 보를 제작하고 휨에 의하여 파괴시까지 실험하였다. 하중-수직변위 분석결과, 큰 형상비의 강섬유를 사용하여도 소형보의 실험(Moon et al, 2013)과 달리 보의 인성거동을 증진시키는 효과는 거의 없는 것으로 나타났다. 극한상태에서 강섬유는 균열폭 7 mm까지 하중을 저항하는 것으로 확인되었다. 또한, 기존의 SFRC 보의 휨강도예측모델과 실험결과를 비교한 결과, SFRC 보의 휨강도를 최대 20배까지 과소평가하고 있는 것으로 나타났다. 그러나, TR No. 63 모델(Concrete Society, 2011)은 다른 모델에 비하여 근사하게 휨강도를 예측하는 것으로 확인되었다. 강섬유의 분포에 대한 분석결과, 소형보에서 보다 실제 규모의 보에서 강섬유의 분산도가 훨씬 개선되는 것을 확인하였다.